1. Technical Field
This invention relates to audio headphones, and more particularly, audio headphones having active noise suppression.
2. Related Art
Headphones are worn by an end user to enable the user to listen to audio, such as music or speech, and to listen to other useful signals. Earpieces of some headphones include components or elements to dampen or reduce the interfering effect of ambient noise, such as noises occurring at a construction site, road noises, or noises occurring around or within a vehicle. While some of these headphones dampen or reduce high-frequency ambient noise they still permit low-frequency ambient noise to enter the earpiece undampened.
Other headphones are configured such that an earpiece loudspeaker actively outputs a signal that is substantially inverse to the noise penetrating from the outside of the earpiece so that the low frequency noise is substantially canceled out before the noise enters the end user's ear. Some active noise suppressing headphones include microphones that are generally arranged on a front outside portion of one or both headphone ear pieces. These headphones operate on surrounding ambient noise through the external microphones and a separate control unit in combination with a radio and a number of control buttons. Other active noise suppressing headphones sense ambient noise with an external microphone and compensate for the sensed ambient noise with a loudspeaker internal to a headphone ear piece and an analog filter with a transfer function. Yet other active noise suppressing headphones use separate microphones paired with separate specified filters or filter hands to reduce ambient noise. The user of these noise suppressing headphones selects through switches, depending on the circumstances, whether the first filter or the second filter is used for noise suppression. Yet other active noise suppressing headphones input ambient noise received at a microphone through an adaptive filter. In these noise suppressing headphones, the adaptive filter output is aligned in with the incidence direction of the ambient noise through the use of an error microphone positioned by a loudspeaker membrane.